High-pressure radical process has been known for long as a process for producing polyethylene having branching structure by polymerization of ethylene. According to this process, a low-density polyethylene having complicated branch structure including short-chain branches and long-chain branches is obtained by homopolymerization of ethylene. However, since the high-pressure radical process utilizes a radical reaction, the branching structure of the resulting ethylene polymer can hardly be controlled, and mechanical strength of the ethylene polymer is not necessarily satisfactory.
One terminal of each polymer chain of the ethylene homopolymer obtained by the high-pressure radical process is methyl group and another terminal is methyl group or unsaturated group due to the polymerization mechanism. It is known that there is vinyl group, vinylidene group or the like as one terminal of the polymer chain, and a polyethylene having vinylidene group structure at one terminal is higher in heat stability of resin at molding as compared with a polyethylene having vinyl group structure at one terminal (e.g., Patent Document 1).    [Patent Document 1] JP-A-8-34819